Aleister Crowley (1875–1947) was born to a devout English fundamentalist Christian family of the Plymouth Brethren sect, now considered a cult, to which he adhered until his father, Edward, died in 1887 when Crowley was 12, at which time he became a committed Satanist, despite having virtually memorized the Bible. Crowley had been abused in a private Christian boarding school, documented in his autobiographical essay, “A Boyhood in Hell.” Crowley accepted Buddhism about 1902 under the influence of his friend and mentor, Allan Bennett, who later became a Burmese Buddhist monk, taking the name of Bhikku Ananda Metteyya. Crowley published a number of significant Buddhist writings about this time, including “Pansil,” “The Three Characteristics,” “Science and Buddhism,” and The Sword of Song, the latter reviewed by G.K. Chesterton no less. Crowley described himself as a “Buddhist rationalist,” and incorporated many Buddhist principles and practices into his system of Scientific Illuminism, codified in the organization of the A∴A∴, which Crowley founded with George Cecil Jones circa 1907. Crowley subsequently converted to his own religion of Thelema in 1909, when he wrote a long poem entitled Aha!, described by Crowley as “my greatest magical poem.” However, he realized the historical relativity of the Law of Thelema during his Esopus Island retreat in 1918, after which he appears to follow Lingbao Taoism, a hybrid of Taoism and Buddhism. This experience presaged the opening of the grade of Ipsissimus (the highest grade of the A∴A∴), which Crowley subsequently claimed in 1921 (it appears that Crowley claimed the grade of Magus in 1916, though sources vary between 1914 and 1919). Crowley wrote his own paraphrase of the Classic of Purity (Qingjing Jing), a Lingbao classic, attributed to Ge Xuan (164-244 CE), during this retreat, as well the Tao Te Ching and the I Ching, which he used for divination throughout his life. Crowley also identified himself with Ge Xuan, the founder of the Lingbao School.
(quoted from an answer I wrote to a question in Quora)
The Secret Door 